Yoga and meditation practitioners claim that breathing can calm the mind. Skeptics may think this is all in their heads. Well, it is. In the brainstem, to be precise.
Researchers have found a subgroup of about 175 neurons in the brainstem of mice that seem to monitor breathing rhythms and influence how calm or aroused the animal is, according to the study published today in Science.
These neurons are found in the breathing control center in the brainstem, surrounded by several thousand neurons that generate the breathing rhythm used by respiratory muscles.
The newly identified neurons, however, are not involved in generating breathing rhythms. Mice that lack these neurons are still able to breathe, but become exceptionally calm. When put in a new environment with a lot of exciting odors that normally incite the animals to explore, these mice take a laid-back approach and spend most of their time sitting and grooming.
The finding reveals one way that neurons behind a basic autonomous function such as breathing can communicate with areas governing higher-order mental states. It could explain why yogis and meditators can use slow, controlled breathing to achieve tranquil states, and why people in stressful situations or during panic attacks may benefit from taking deep breaths.
In other words, just like your mental state influences how you breathe, your breathing rhythm can also influence how you feel.
“We think this is a two-way connection,” Kevin Yackle, a researcher now at UC-San Francisco and the study’s co-author, tells mental_floss. “These neurons are monitoring the breathing activity and then relaying it back to the rest of the brain to indicate what the animal is doing. This breathing signal then influences the brain state of the animal.”
A SERENDIPITOUS FINDING
This was an unexpected finding for the researchers, Yackle says.
The study’s goal was to paint a more accurate picture of how each type of neuron contributes to breathing. Understanding the details of this machinery can have important medical implications, Yackle says. In cardiology, for example, our detailed understanding of how the cardiac rhythm is generated has led to the development of medications that can control heart muscle contractions. “But when you think about breathing, we don't have any ways for pharmacologically controlling it,” Yackle says. Such a pharmacological approach could help preterm infants, for example, whose neural circuits for breathing are not fully developed, leaving them in need of mechanical ventilation.
The team started out by looking at a cluster of neurons called the preBötzinger Complex, which controls breathing rhythms. It was discovered in 1991 by Jack Feldman, a professor of neurobiology at UCLA and the co-author of the current study. (The same team recently revealed the biological importance of sighing.) The goal was to identify the different subsets of neurons within this cluster and find what each type of neuron does to contribute to breathing.
The researchers landed on a small group of 175 neurons with a particular genetic profile that suggested a crucial role in generating the breathing rhythm. But killing these cells in the brainstem of mice proved that their guess was wrong. The mice continued to breathe normally.
“I was really disappointed,” Yackle recalls. “But we had put so much effort in the project by that point that I just continued looking at it, trying to find what was happening.”
However, Yackle soon noticed one subtle difference: The mice were breathing more slowly.
An illustration of the pathway (green) that directly connects breathing center to arousal center and rest of the brain. Image Credit: Kevin Yackle, Lindsay A. Shwarz, Kaewen Kam, Jordan M. Sorokin, John R. Huguenard, Jack L. Feldman Liqun Luo, and Mark Krasnow
A CLOSED LOOP
One way to explain a shift like that was to imagine that the breathing pattern was influenced by the mental state of the animals. The researchers found more evidence for this idea.
Usually, mice explore a new cage by sniffing all throughout it. If the idea about a connection between breathing and the rest of the brain is true, then these bursts of short deep breaths could reinforce the alert state of the exploring animals, creating a feedback loop. But if a key component in this chain is missing, the loop is broken. When the researchers tested this theory, as expected, the mice that lacked the subgroup of neurons appeared less aroused than their unaffected cagemates when put in stimulating environments. The animals’ brain waves patterns, measured by EEG, also suggested a calm mental state.
Tracing the neurons revealed that they connect to another part of the brainstem, locus coeruleus, which is known for its role in physiological responses to stress, as well as alertness and attention.
“We think that these neurons in the breathing center are relaying the breathing signal to the locus coeruleus, and by doing this they are basically sending a signal throughout many parts of the brain that then can cause change in arousal,” Yackle says.
The authors note that panic attacks triggered by respiratory symptoms are responsive to clonidine, a drug that "silences" the locus coeruleus. Deep breathing could play a similar role, quelling the arousal signals coming from this subgroup of respiratory neurons to the locus coeruleus.
"Although breathing is generally thought of as an autonomic behavior, higher-order brain functions can exert exquisite control over breathing," they write. "Our results show, conversely, that the breathing center has a direct and powerful influence on higher-order brain function."
It would be challenging to test this directly in humans. But indirect evidence from other studies suggests that breathing can influence brain states.
For example, sleep researchers have shown that in sleeping people, a change in breathing pattern sometimes precedes periods of brain activity that resemble an alert or wakeful state.